This invention relates generally to valve control devices for engines and, more particularly, to valve control devices and related methods of valve control for valves associated with internal combustion engines that utilize push rods. Proper control of engine valves is well recognized as an essential means of maximizing performance characteristics of many internal combustion engines. Therefore, a considerable amount of effort has been expended in the development of valve control devices which efficiently and effectively regulate the valves of internal combustion engines.
A variety of valve control devices for internal combustion engines are known. Typically, they include a rocker arm which is engageable with a push rod and a valve stem which is associated with one or more valve springs. Movement of the camshaft of the engine actuates the push rod, thereby pivoting the rocker arm against the stem of the valve and the biasing force of the spring or springs so as to temporarily open the valve.
FIG. 9 depicts a representative example of a conventional valve control device for an automobile engine which engine includes a cylinder head 10 having a valve 12 whose stem 14 extends through the cylinder head and through the valve guide 15 and is capped by a retainer 16. A rotatable camshaft 18 having a cam lobe 20 with a neutral circular surface 22 and an arcuate lifting apex 24 also extends axially beneath the cylinder head. The valve control device includes a pair of valve springs 26 and 27 and a rocker arm 28 which is pivotally connected to the cylinder head through shaft 30 and associated with a reciprocable push rod 32 that extends longitudinally through a thoroughbore 34 in the cylinder head 10. The valve springs 26 and 27 are compression springs which are situated around the protruding portion of the stem 14 and against the retainer 16, thereby holding the valve 12 projected in its normal closed position and appropriately maintaining the seat pressure exerted on the valve 12. (See, FIG. 9). Valve spring 26 is also stronger than valve spring 27.
The rocker arm 28 includes a contact roller 36 which is rotatably mounted on a roller shaft 38 situated at the end of the rocker arm that is adjacent to the stem 14. The top end of the push rod 32 is received within a concavity defined in the rocker arm 28. When the push rod is aligned with the neutral circular surface 22 of the cam lobe 20, the contact roller of the rocker arm is typically almost in contact with the stem 14.
As the cam lobe 20 rotates, its arcuate apex 24 moves the push rod 32 longitudinally upward such that the contact roller 36 of the rocker arm 28 impacts the stem 14 as the rocker arm pivots. Consequently, the contact roller 36 pushes the stem 14 of the valve 12 against the combined biasing force of the valve springs 26 and 27 and the valve is opened. As the cam lobe continues to rotate, the push rod moves in relation to the arcuate apex such that the now compressed valve springs expand and force the push rod longitudinally downward by thrusting the side of the rocker arm adjacent to stem 14 upward or clockwise (See, FIG. 9). The push rod thus returns to its neutral position.
Other variations of valve control devices also exist, including devices that have a valve lifter 37 situated at the bottom of the push rod for transmitting the action of the camshaft to the push rod. (See, FIG. 9).
While devices of this nature have performed reasonably well in terms of valve regulation, they have a number of drawbacks. For instance, the rocker arm that is a component of such devices tends to be damaged too frequently due to the stress induced on it by repeated rapid engagement with the valve stem. The end of the valve stem may also tend to wear or fail too quickly due to the biasing force of the valve springs acting directly on the valve. Moreover, to the extent that energy from the engine is utilized to actuate such devices upon their interaction with the camshaft, less energy from the engine is available for moving or otherwise operating the motor vehicle. This utilization of energy tends to have a negative effect on performance characteristics of the engine, on overall fuel economy, and on the engine's output of pollutants into the atmosphere as well as on engine and oil operating temperature and overall wear and tear on the engine. These disadvantages have prompted the automobile industry to employ overhead cam assemblies.
It should, therefore, be appreciated that there exists a definite need for a valve control device, and related method of valve control, which is capable of enhancing certain performance characteristics of an internal combustion engine utilizing push rods and the useful life of valve control devices, and which tends to improve fuel economy and lessen the engine's output of certain pollutants, and which further tends to reduce oil and engine operating temperature and wear and tear on the engine.